Fluorocarbon derivatives (sometimes called organofluorine compounds or fluorochemicals) are a class of substances containing portions which are fluorocarbon in nature, e.g. hydrophobic, oleophobic, and chemically inert, and portions which are organic or hydrocarbon in nature, e.g. chemically reactive in organic reactions. The class includes some substances which are familiar to the general public, such as those which give oil and water repellency and stain and soil resistance to textiles, e.g. Scotchgard.TM. carpet protector. Other substances of the class have various industrial uses, such as reducing the surface tension of liquids, reducing evaporation and flammability of volatile organic liquids, and improving the leveling of organic polymer coatings. Examples of industrial substances are the Fluorad.TM. fluorochemical surfactants described in 3M Company trade bulletin 98-0211-2213-4 (38.3) BPH, issued March, 1988.
Conventional fluorochemicals can be prepared from precursors such as fluoroalkyl iodides, fluoroalkyl carboxylic acid fluorides, and fluoroalkyl sulfonyl fluorides. See for example, "Organofluorine Chemicals and Their Industrial Applications", R. E. Banks, Ed., Ellis Horwood, Ltd., Chichester, England, 1979, pp. 214-234.
Some perfluoroalkyl iodides can be prepared by telomerization of C.sub.2 F.sub.5 I or (CF.sub.3).sub.2 CFI with C.sub.2 F.sub.4 yielding C.sub.2 F.sub.5 (C.sub.2 F.sub.4).sub.n I or (CF.sub.3).sub.2 CF(CF.sub.2 CF.sub.2).sub.n I, respectively, where n is typically from 1 to 4. See R. E. Banks, supra. All of the perfluoroalkyl iodides obtained from (CF.sub.3).sub.2 CFI contain perfluoroalkyl groups with a terminal branch, and such branched-chain perfluoroalkyl groups will hereinafter be represented by "R.sub.fb ". All of the perfluoroalkyl iodides obtained from C.sub.2 F.sub.5 I contain straight-chain perfluoroalkyl groups without branches, and such straight-chain (or "linear") perfluoroalkyl groups will hereinafter be represented by "R.sub.fs ". For brevity, "R.sub.f " will hereinafter be used to represent a perfluoroalkyl group with either a straight or a branched-chain. Perfluoroalkyl iodides can be converted into other functional (or reactive) materials, for example by the following illustrative schemes.
R.sub.f -I+CH.sub.2 .dbd.CH.sub.2 .fwdarw.R.sub.f -CH.sub.2 CH.sub.2 --I PA1 R.sub.f -CH.sub.2 CH.sub.2 --I+H.sub.2 O.fwdarw.R.sub.f -CH.sub.2 CH.sub.2 --OH PA1 R.sub.f -CH.sub.2 CH.sub.2 --I+H.sub.2 NC(S)NH.sub.2 .fwdarw.R.sub.f -CH.sub.2 CH.sub.2 --SH PA1 R.sub.f -CH.sub.2 CH.sub.2 --I.fwdarw.R.sub.f -CH.dbd.CH.sub.2
The alcohol, thiol, and olefin derivatives of the above schemes can be further converted to a great variety of derivatives, e.g., acrylates and polymers thereof, sulfates and salts thereof, carboxylic acids and esters thereof, etc. These further derivatives retain the original structure of the R.sub.f group, that is, the R.sub.f group remains either straight or branched.
Functional materials derived from telomer iodides will (as stated above) contain either 100% straight-chain (R.sub.fs) or 100% branched-chain (R.sub.fb) perfluoroalkyl groups. Contradictory data have been reported in the literature regarding the relative advantage of straight-chain versus branched-chain perfluoroalkyl groups. In U.S. Pat. No. 4,127,711 (Lore et al.) perfluoroalkyl straight-chains are said to be preferred for textile applications, whereas in U.S. Pat. No. 3,525,758 (Katsushima et al.) it is disclosed that surfactants containing 100% branched-chain perfluoroalkyl groups are more effective than surfactants containing straight-chain perfluoroalkyl groups in lowering the surface tension of aqueous solutions. However, it has generally been accepted that among fluorinated surfactants of the same carbon number, straight-chain products generally give lower surface tension in aqueous solutions. Banks, supra at 222-223, describes that, except at very low concentrations (less than 0.01% or 100 ppm), lower surface tension is attained with straight-chain fluorochemicals. Additionally, an article written by Bennett and Zismann (J. Phys. Chem., 71, 1967, p. 2075-2082) discloses that a condensed monolayer of a fully fluorinated straight-chain alkanoic acid has a lower critical surface energy than its terminally branched analogue with the same chain length.
In addition to the telomerization procedure described above, another method of producing many fluorochemicals or their precursors is the fluorination process commercialized initially in the 1950s by 3M Company, which comprises passing an electric current through a mixture of the organic starting compound and liquid anhydrous hydrogen fluoride. This fluorination process is commonly referred to as "electrochemical fluorination" or "ECF". Some early patents describing such technology include U.S. Pat. No. 2,519,983 (Simons), U.S. Pat. No. 2,567,011 (Diesslin et al.), U.S. Pat. No. 2,666,797 (Husted et al.), U.S. Pat. No. 2,691,043 (Husted et al.), and U.S. Pat. No. 2,732,398 (Brice et al.); they describe the preparation of such fluorochemical compounds as perfluoroalkyl carbonyl fluorides, e.g. C.sub.4 F.sub.9 -COF, and perfluoroalkyl sulfonyl fluorides, e.g. C.sub.4 F.sub.9 -SO.sub.2 F, and derivatives thereof.
When perfluoroalkyl carbonyl fluorides and perfluoroalkyl sulfonyl fluorides are prepared by electrochemical fluorination (ECF) of appropriate hydrocarbon precursors, the resulting products are mixtures of compounds, where some of said compounds contain a straight-chain perfluoroalkyl group, e.g., R.sub.fs -SO.sub.2 F, and others of said compounds contain a branched-chain perfluoroalkyl group, e.g., R.sub.fb -SO.sub.2 F. Such mixtures of compounds result even when the starting materials contain only compounds with straight-chain alkyl groups. Such mixtures of compounds, e.g. a mixture of R.sub.fs -SO.sub.2 F and R.sub.fb -SO.sub.2 F, can be represented, for brevity, by the formula, R.sub.fsb -SO.sub.2 F, which formula represents a mixture of compounds. The "sb" subscripts indicate that the formula represents a mixture of compounds, that is, a mixture of R.sub.fs -SO.sub.2 F and R.sub.fb -SO.sub.2 F.
ECF-derived acid fluorides can be converted into other functional materials, for example by the following illustrative schemes. ##STR1##
Each R.sub.fsb containing formula, e.g., R.sub.fsb -COF, represents ECF derived mixtures which contain some compounds with a straight-chain perfluoroalkyl group and other compounds with a branched-chain perfluoroalkyl group.
U.S. Pat. No. 2,950,317 (Brown et al) describes a process for the preparation of fluorocarbon sulfonyl chlorides from the corresponding fluorocarbon sulfonyl fluorides.
An article by Park et al. (23, J. Org. Chem, 1166-1169 (1958)) describes the preparation of certain fluorochemical compounds with three or less fully-fluorinated carbon atoms. Compounds described include n-C3F.sub.7 --CH.sub.2 CH.sub.2 --I and n-C3F.sub.7 --CH.sub.2 --CO.sub.2 H.